Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a multi-function peripheral incorporating the aforementioned devices, to which an electrophotographic system is applied.
Description of the Related Art
Conventionally, an image forming apparatus to which an electrophotographic system is applied, such as a copying machine, a printer, a facsimile, or a multi-function peripheral incorporating the aforementioned devices, forms an electrostatic latent image on a photoreceptor by irradiating the photoreceptor with a light beam corresponding to image data from a light source, and scanning and exposing the photoreceptor. Further, the image forming apparatus supplies a developer to the electrostatic latent image by a developing unit to make the electrostatic latent image noticeable as an image, and transfers the image from the photoreceptor to a sheet as a recording medium, thereby to form the image on the sheet.
When the temperature around the apparatus main body is sharply raised by an air conditioning facility or the like after the image forming apparatus is left at a low temperature, the temperature of an atmosphere in the apparatus sharply rises from a low temperature to a high temperature. When the sharp temperature rise of the atmosphere in the apparatus is caused, temperatures of components in the apparatus can less easily follow the temperature change of the peripheral environment in a short time. Therefore, condensation may be caused on surfaces of the components.
Further, in a case where sheets having absorbed humidity are passed in large quantities, the humidity in the apparatus sharply rises and the condensation may be caused on the surfaces of the components in the apparatus. In such a case, the condensation caused on an optical component and the like in an optical scanner that emits a light beam from a laser light source causes deterioration of optical characteristics of the light beam that scans and exposes the photoreceptor.
In contrast, Japanese Patent Laid-Open No. 1993-182227 relates to an image forming apparatus that suppresses the condensation on optical components in an optical scanner, and discloses a configuration to house optical components including a semiconductor laser or a reflection mirror in a box-like optical unit, and seals the inside of the optical unit. Accordingly, in the image forming apparatus of Japanese Patent Laid-Open No. 1993-182227, an atmosphere at a raised temperature can be prevented from coming in contact with the optical component at a dew-point temperature or less, and the condensation on the optical components including the semiconductor laser and the like can be prevented.
However, Japanese Patent Laid-Open No. 1993-182227 has a problem that, because the external surface temperature of an optical unit easily becomes the dew-point temperature or less, the condensation is caused on the external surface of a light passing surface of the optical unit, and optical characteristics of the light beam are deteriorated, resulting in a decrease in a required light quantity to a photoreceptor.
Further, Japanese Patent Laid-Open No. 2005-338576 relates to an image forming apparatus, and discloses a configuration to provide a heater unit between a light beam scanning unit and an image forming unit, and heat an atmosphere between the light beam scanning unit and the image forming unit. Further, Japanese Patent Laid-Open No. 2005-338576 discloses a configuration to cause a heated atmosphere to flow from a lowermost portion to an uppermost portion of a plurality of emission windows arrayed in an up and down direction with respect to an installation surface of an apparatus main body, to warm up the plurality of emission windows with the heated atmosphere, thereby to suppress occurrence of the condensation on the plurality of emission windows.
However, in Japanese Patent Laid-Open No. 2005-338576, an increase in manufacturing cost is incurred to newly add a heater unit. Further, to prevent the condensation in an extremely cold region, the heater needs to be ON on a constant basis, and thus there is a problem from the aspects of cost and energy saving.